Brushless dc adjustable speed drive with static regenerative dc motor control

ABSTRACT

For a brushless direct current motor there is provided a static adjustable speed control circuit including an SCR converter for controlling the average voltage applied to the motor windings by phase control of current flowing directly from a multi-phase power source and for commutating the current through the motor winding to maintain the proper current flow direction and torque. The SCR converter is controlled as a function of rotor position, a-c line input conditions, phase advance and SCR converter voltage output. A voltage feedback signal from the converter output is compared to a reference voltage to derive a comparison signal used to adjust the phase advance and thereby control the average voltage applied to the motor terminals. The polarity of the comparison signal determines whether motoring action or regeneration is to occur. Current feedback from the input lines is used to prevent combinations of SCRs from &#39;&#39;&#39;&#39;turning on&#39;&#39;&#39;&#39; and short circuiting the load.

United States Patent Kolatorowicz [451 July 18,1972

[54] BRUSHLESS DC ADJUSTABLE SPEED DRIVE WITH STATIC REGENERATIVE DCMOTOR CONTROL [72] Inventor: Edwin E. Kolatorowia, Erie, Pa.

[73] Assignee: General Electric Company [22] Filed: July 14, 1970 [21]Appl. No.: 54,703

[52] US. Cl. ..3l8/254, 318/439, 318/138 [51] InLCl. "02k 29/00 [58]Field 01 Search ..318/138, 254, 439, 696, 685

[56] References Cited UNITED STATES PATENTS 3,418,550 12/1968Kolatorowicz et al ..318/ 128 2,193,914 3/1940 Alexanderson ..318/l381,937,377 11/1933 Alexanderson.... ..318/l38 1,976,463 10/1934 Sabbah.....318/l38 2,193,932 3/1940 Mittag ..3l8/l38 CURRENT FEED BACK PrimaryExaminer-G. R. Simmons Attorney-James C. Davis, Jr., Edward W. Goebel,.lr., Frank L. Neuhauser, Oscar B. Waddell and Joseph B. Forman [57]ABSTRACT For a btushless direct current motor there is provided a staticadjustable speed control circuit including an SCR converter forcontrolling the average voltage applied to the motor windings by phasecontrol of current flowing directly from a multi-phase power source andfor commutating the current through the motor winding to maintain theproper current flow direction and torque. The SCR converter iscontrolled as a function of rotor position, we line input conditions,phase advance and SCR converter voltage output. A voltage feedbacksignal from the converter output is compared to a reference voltage toderive a comparison signal used to adjust the phase advance and therebycontrol the average voltage applied to the motor temiinals. The polarityof the comparison signal determines whether motoring action orregeneration is to occur. Current feedback from the input lines is usedto prevent combinations of SCRs from turning on" and short circuitingthe load.

3 Claims, 20 Drawing Figures I PATENIEnJuu em:

saw on HF 13 POSITION CONTROLS m rm mm F/G. 5b

PHASE CONTROLS SCR FIRING SIGNAL INVENTOR EDWIN E. KOLATOROWlCZ ATTORNEYPATENTED m? I 3.678.358

sum as UF--13 I-2 l-3 2-3 2-I 3-l V37-2 O 60 I I80 240 300 360 CEMFHCOMMUTATION ADVANCE "o BEFORE MOTORING COMMUTATION 1/ AT I50 POINTTURNED"'ON" AT [50 "0N" DURING ENTIRE 'COMMUTATION PERIOD "0N" DURINGENTIRE coIvIIvIuTATIoN PERIoD a REGENERATING COMMUTATION AT |50 POINT M3"0N" BEFORE TURNED "0N" AT l50 INVENTOR EDWIN E. KOLATOROWICZ A'I'TIIIINl-ZY PATENTEDJummz 3.678.358

SHEET U60F13 POSITION INVENTOR EDWIN E. KOLATOROWCZ ATTOR N EYPATENTEnJuLwmz 3,678,358

sum 07 or 13 EDWIN E. KOLATOROWICZ g W7 Z/ 7 PATENTEU JUL! 81972 sum 090F 13 4 m 2 R V G .B G 2 2 T B T 0 O 2 8 m 4 W 2 m m m w PHASE CONTROLT! M l NG mvsrwon EDWIN E. KOLATOROWICZ PATENTEDJUL 8 I972,

223 22| 224 1- r r M GATE XFMR ZZ SCILLATOR INPUT GATE DRIVER 20v 11 3?POSITION i l CONTROL 228 230 INPUT 23s (i1-F+31-R) PHASE coumou. 529INPUT 235 Ai SHEET 10 [1F POSITION LOGIC ZID 214 P2 GATE LOGIC 20 V ODELAYED INVENTOR EDWIN E. KOLATOROWICZ awm ATTORNEY PATENTED JuL18|9123.678.358

' SHEET 11 0F 13 OUTPUT g 303 CLAMP CT-C 300 A 7 30s 5% 3|0 30s COMMONCURRENT. FEED BACK I 245 j Z 244 24o T T v I 26v DELAYED OSCILLATOR 242OSCILLATOR OUTPUT F /G. 15

INVESTOR 4 EDWIN E. KOLATOROWICZ BRUSHLESS DC ADJUSTABLE SPEED DRIVEWITH STATIC REGENERATIVE DC MOTOR CONTROL CROSS REFERENCES TO RELATESAPPLICATIONS This invention relates to brushless adjustable speed motordrive systems of the general type described in an article entitled TheThyratron Motor, published by Alexanderson and Mittag, in ElectricalEngineering, November, 1934, PP, l,5l7l,523 and of the type described inmy US. Pat. No. 3,418,550, issued Dec. 24, 1968, and assigned to theassignee of the present invention. More particularly, the presentinvention relates to improvements in brushless adjustable speed motordrive systems of the type disclosed in my aforementioned US. Pat. No.3,418,550.

The present invention relates to controls for d-c motors and provides astatic control circuit which permits braking of the d-c motor by meansof regeneration. The term static signifies that the control utilizeselectronic components rather than rotating machinery to apply andcontrol power to the motor.

BACKGROUND OF THE INVENTION My aforementioned US. Pat. No. 3,418,550discloses a practical brushless direct current motor adjustable speeddrive system capable of supplying considerable power, for instance, inthe range of to 100 (or more) horse power, while being competitive withknown drive systems both as to size and cost, as well as efficiency withrespect to power consumption, maintenance and reliability. The SCRconverter of that patent is controlled by logic-gating means to combinethe functions of power-line phase selection and the shaft positioncommutating function. The same SCRs participate in both functions.

The logic-gating circuits include multiple inputs which determine thepresence of a single output to control one of the SCRs. Each of thesegating circuits comprises a blocking oscillator whose output whenpresent triggers one SCR, but whose triggering is controlled by multipleinputs, one of which is enabled by position sensing means, and others ofwhich are enabled by phase control means referenced to the power lines.The particular SCR which is triggered is selected by the phase controlmeans. The phase control consists of six unijunction transistor circuitssynchronized to the three-phase a-c line with a delta-star transformercircuit. To achieve a continuous signal of sufficient width (120), theunijunction transistor triggers a small SCR. The reset is controlled bythe a-c synchronizing voltage in such a manner that the width whichvaries with advance is never below 120 in the operative range. Thisarrangement is only desirable for non-regenerative operation since, ifthe signals are 120 wide at maximum retard, an advance of more than 60would cause firing signals to an incoming and outgoing SCR connected tothe same line and short circuit the load.

Many applications of d-c motors require braking of the motor duringoperation. For example, extremely accurate speed control may requirethat the motor be braked as soon as it exceeds a desired speed. Otherexamples include d-c motors subjected to overhauling loads, as in crane,hoist and elevator service. The methods and apparatus employed forcontrolling such braking action have presented problems for many years.Where economy is desired, a simple mechanical brake is employed, butbraking action is difficult to control. The use of an externalelectro-mechanical brake, such as an eddy current brake overcomes someof the problems associated with a mechanical brake, but on the whole,external brakes have generally proved unsatisfactory.

As a result, resort has been made to internal electrical braking such asplugging, dynamic braking or regenerative braking. Plugging involves thereversal of motor armature voltage and current and results in highcirculating currents in the armature circuit. As a result of largethermal strains on the motor, repeated braking operations cannot beperformed without danger of excessive heating and damage to the motor.In dynamic braking, a resistor is placed in the armature circuit. Themotor in effect becomes a d-c generator supplying power LII to theresistor load. While the resistor limits the armature current and hencethe thermal strain on the motor, it also decreases thc effectiveness ofthe braking action, particularly at slow speeds. Thus, such anarrangement is not desirable where extremely accurate speed control isrequired or motors control low speed loads as in crane, hoist andelevator service.

Regenerative braking of d-c motors also employs the motor as agenerator, similar to dynamic braking. However, it differs therefrom inthat in regenerative braking the power generated by the motor isreturned to the active power source for the motor rather than beingcirculated through a passive resistor load. Power may be regenerated byreversing the polarity of the armature voltage while maintainingarmature current flow in the same direction or by reversing armaturecurrent flow while maintaining the polarity of the armature voltage. Ineither case, the motor that was formerly a load becomes a power source.

In a regenerative braking system, braking may be accomplished rapidlyand on a permanent basis as opposed to plugging and dynamic brakingwhich function for isolated stopping conditions. Also, with propercontrol, armature current may be limited so as to avoid excessivethermal strain on the motor.

For the foregoing reasons, regenerative braking is generally consideredto be the most desirable method of braking. In the past the moreconventional approach in prior art static regenerative d-c motorcontrols has been to reverse armature current while maintaining theterminal voltage of the d-c motor the same. However, this hasnecessitated two power supply circuits, one for each direction ofcurrent flow. This, of course, substantially increases the cost and alsothe complexity of the power circuit.

SUMMARY OF THE INVENTION These and other disadvantages of the prior artare overcome by the present invention in which the armature is suppliedfrom a controlled rectifier converter and in which the torque of themotor may be continuously varied from a maximum positive value to amaximum negative value with the controlled rectifier converter beingcontrolled to effect retardation of the motor when the motor is beingdecelerated from a high speed to a lower speed, or when the motor isoverhauled by its load.

Another important object of the present invention is to combine thefunctions of power-line phase selection with shaft position commutationand to provide a static control drive circuit in which the samecontrolled rectifiers participate in both functions without thenecessity of additional power SCRs to permit the system to regenerate.

These and other objects and their attendant advantages will becomeapparent from the following description of the invention which providesan adjustable speed drive having controlled rectifiers arranged toeommutate current to the stationary armature windings of a salient polerotating field machine wherein the primary source of power is apolyphase a-c supply and speed is adjusted by phase-controlling thefiring of the controlled rectifiers of the conversion unit connected tothe motor armature windings. A position sensor associated with the motorgoverns the progressive energization of the motor windings, while thecommutation of the controlled rectifiers is accomplished by the actionof the a-c supply voltage and motor counter E.M.F.

DRAWINGS For a fuller understanding of the invention, the description ofthe construction and mode of operation of the control circuits of thepresent invention should be considered in connection with the followingdrawings wherein like parts are identified by like reference charactersthroughout the several views, and which illustrate, by way of example,one illustrative embodiment of the present invention:

FIG. 1 is a diagram of the brushless d-c adjustable speed driveillustrating in block diagram form the static regenerative d-c motorcontrol of the present invention;

FIG. 2 is a block diagram showing in detail the switching logic stageswhich make up the d-c motor control of the present invention;

FIG. 3 is a schematic diagram of the SCR conversion and motor controldrive circuit of the present invention;

FIG. 4 is a graphical representation of motor leg currents;

FIGS. 5a, 5b and 5c illustrate, respectively, position, phase controland firing signal relationships;

FIG. 6 is a graphical representation of CEMF commutation with 30advance;

FIGS. 7a and 7b illustrate regenerating motor leg commutation at the 150point;

FIG. 8 is a detailed block diagram of the position logic, gate logic andgate drive circuits ofthe present invention;

FIG. 9 is a schematic diagram of the phase control ring circuit of thepresent invention;

FIG. 10 is a schematic diagram of the phase shift and filter controlcircuits of the present invention;

FIG. 11 is a schematic diagram of the phase control timing circuit ofthe present invention;

FIGS. 12 and 13 are schematic diagrams of single stages of the positionlogic and gate logic NAND circuits of the present invention;

FIG. 14 is a schematic diagram of the gate driver circuit of the presentinvention, while FIG. 15 illustrates schematically the associatedoscillator circuit;

FIG. 16 is a schematic diagram of the current feedback circuit of thepresent invention;

FIG. 17 is a schematic diagram of the coordination circuit of thepresent invention; and

FIG. 18 illustrates schematically the position inverter, directionsensing and F/R flip-flop circuits of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, andin particular to FIG. 1, reference character 10 identifies generally ad-c motor having a permanent magnet rotor. The stationary armature isprovided with three windings a, b and c each of which has one endconnected to a common bus bar in a conventional manner. The other endsof these windings are connected to conductors l1, l2 and 13,respectively, which are in turn connected to intermediate tappingpositions on reactors 14, 15 and 16.

The particular type of motor used can vary and the illustrativeembodiment given by way of example has been selected for the purpose ofeliminating any need to transfer current into rotating windings. Thistype of motor includes a stationary armature having plural windingswhich are externally commutated in order to provide a rotating fieldwhose rotation is controlled by the shaft position sensor to lead therotor by about 90 electrical degrees within the motor speed range. Anynumber of different motor structures can be used. For example, thepermanent magnet rotor can be replaced by a wound salient-polestructure. To eliminate slip rings, a coaxial transformer can be used totransfer alternating current power to the rotating member, andreetifiers mounted directly on it can perform the required conversion todirect current.

Reactor windings 14, 15, and 16 are provided for the purpose ofsmoothing the current delivered to the motor from power lines A, B, andC. windings 14, 15 and 16 also serve to limit short circuit current inthe event of faulty SCR commutation. To this end, the reactor windingsare closely coupled so that motor leg commutation is not impeded. Themotor commutation is further assisted by amortisseur bars (not shown)inserted in the motor as described in my aforenoted U.S. Pat. No. 3,4l8,550. These bars serve the purpose of reducing the eommutatingreactance appearing at the motor winding terminals in a manner which iswell known in the art.

The power drive to the motor 10 is supplied from a multiphase a-c powerline including phases A, B and C." Because of the fact that the rotationrate of output shaft 18 of the motor is not in any way related to thefrequency of the a-c power line, the present invention provides forline-phase switching by which the voltage applied to the motor windingsthrough conductors 11, 12 and 13 from the a-c power lines isinstantaneously selected by phase-control means so as to have thecorrect polarity, and also to be coupled to the winding at a phaseinstant which is correct to provide the average voltage necessary tomaintain the selected motor speed. In the illustrative embodiment, boththe phase selecting function and also the shaft position eommutatingfunction are carried out by the SCR conversion assembly 17.

Before proceeding with a detailed description of the logic controlcircuit, a clarification of the nomenclature used in the descriptionwill now be given with reference to FIG. 3. The a-c supply lines, aspreviously indicated, are labeled A," B" and C, while the motorterminals are identified as M1, M2, and M3. The motor terminals M1, M2and M3 are fed from the conversion unit 17 by way of the reactor whichhas three center tap windings 14, 15 and 16, all on a common core.(urrent flowing from the conversion unit into the motor winding Athrough motor terminal Ml flows through reactor terminal Mll. Reactorterminals M21 and M31 feed motor terminals M2 and M3, and motor windingsB and C," respectively. Currents out of motor windings A, B" and C,"return to the reactor terminals M10, M20 and M30, respectively, forcontrolled and properly phased flow into the a-c supply lines A," B" andC" through the appropriate SCRs. Thus it becomes apparent that thoseSCRs connected to one of the reactor terminals M11, M21 or M31 areactive in conducting electric current to the motor 10. Conversely, thoseSCRs tied to one of the reactor terminals M10, M20 or M30 permitcontrolled current flow from the motor 10 to the a-c source.

As shown in FIG. 3, the SCR conversion assembly 17 comprises a quantityof eighteen silicon controlled rectifiers (SCRs), each bearing areference numeral 19 through 36. These SCRs are selectively renderedconductive, several at'a time, through a novel switching-logic system 37as shown in block form in FIG. 1. The switching-logic system 37 takesthe phase information from power lines A, B and C, the shaft-positioninformation from a position sensor 38, a voltage feedback signal fromthe output of converter 17 and a current feedback from the input linesA, B and C and then selects and triggers the appropriate SCRs.

Current feedback is taken from the A, B" and C" input lines from threecurrent transfonners via signal paths 39, 40 and 41 and rectified incurrent feedback stage 42 the output of which is applied to theswitching logic system through line 43. The voltage feedback signal isderived from armature conductors ll, 12 and 13 and after processing inrectifier stage 44 is applied through line 45 to the switching-logicsystem 37 which also receives position signals through line 46. Themomentary phase condition of the A, 8" and C power lines is determinedby phasing transformer stage 47 and the corresponding output signals areapplied to the switching-logic system through conductors 48, 49 and 50.The angular position signal is derived from position sensor 38 driven bymotor 10.

In order to monitor the momentary angular position of the motor shaft18, a position sensor 38 is coupled to and driven by the shaft 18. Thisposition sensor 38 may take the form shown in my aforementioned U.S.Pat. No. 3,418,550 in which the rotor position sensor comprises phototransistors spaced around a circuit board and facing in the direction ofoppositely located light sources placed on the other side of aninterposed light choppcr which is turned by the motor shaft. Thischopper is in the form of a disc having apertures through which thelight sources, such as lamps, light emitting semiconductors or the like,can illuminate the photo transistors. For a six track position sensor,six outputs are provided which control the six groups of SCRs shown inFIG. 3. The six track information can alternatively be generated bythree sensors which are then connected to logic means suitable fordecoding six position-indicating outputs. Amplifying means attached toeach position sensor provides an output signal whenever an aperture inthe light mask disc is opposite the associated photo transistor. Theamplifier connected to that transistor then delivers an enabling signalto a suitable firing circuit means which has its output applied to theswitching-logic circuit.

The invention is not limited to this particular type of position sensingmeans and other forms may be utilized such as, for example, magneticsensing devices, Hall-effect devices, capacitive devices, etc.

The switching-logic system 37 of FIG. 1, detailed in FIG. 2, comprises anumber of stages built around NAND type logic circuits to enable groupsof SCRs to provide regenerative as well as motoring operation of themotor in a most economical and efficient manner. To this end, positionsignals P1, P2 and P3 generated by position sensor 38 are appliedthrough line 51 to position signal inverter stage 52 which inverts theposition signals. Output signals P1, P2 and P3 of inverter 52 areapplied through line 53 to position logic stages 54 and 55. Positionsignals 1 1, Q and F3 are also applied to the position logic stages 54and 55 as well as to the direction sensing circuit or stage 56 throughline 57.

Position logic stages 54 and 55 generate six-track information from thethree track information provided by the position sensor. At the sametime, a forward-reverse (F/R) signal is applied from the FIR flip-flopstage 58 toeach of the stages 54 and 55 through line 59. The outputs ofthe position logic stages 54 and 55 are applied to the gate logic stage60 through lines 61 and 62, respectively. Gate logic stage 60 generatesa single enabling signal for each of the six SCR groups. Actually,however, each SCR group is enabled by two combinations of signals. Onecombination corresponds to motoring operation in the first quadrant andto regenerative operation in the fourth quadrant of operation. The othercombination corresponds to motoring operation in the third quadrant andto regenerative operation in the second quadrant of operation. Thesingle enabling output gate signal for each of the six SCR groups isgenerated in stage 60 and is applied to the SCR converter for firing ofthe SCRs in the proper sequence through gate drivers 64-69. Inputs tothe gate drivers, in addition to the enabling signal applied throughline 70, include the output of oscillator 71 applied through line 71 andthe output of the phase control rings 73 and 77 applied through lines 74and 75.

The phase control system comprises the phasing transformers 47 and itsassociated filters, timing stage 76 and two phase control ring stages 73and 77 which insure that the trigger pulses follow the desired sequenceof operation. The output trigger pulses of the timing stage are appliedto phase control rings 73 and 77 over lines 78 and 79 and are phasedisplaced with respect to each other by 180.

Sync signals are derived in phasing stage 47 and are applied to thephase control rings 73 and 77 over lines 80 and 81, respectively, and tothe timing stage 76 over line 82. The current feedback stage 42 providesa voltage proportional to current flow and also provides a clamp signalfor the FIR flip-flop through a coordination circuit 84. Thecoordination circuit allows four quadrant operation. To this end,direction reference signals are applied thereto from the directionsensing stage 56 through line 85, while current feedback signals fromthe input lines A, B and C, and voltage feedback from the motor windingsare applied through lines 43 and 45, respectively, with a referencecommand input being applied at 87. The output control signal is appliedthrough line 88 to stage 76 to control the average voltage applied tothe motor 10 that its speed may be thereby governed. Signals from thecoordination circuit 84 also control the action of the FIR flip-flop 58,being connected thereto by a line 89.

The operation of the drive circuit will be described first withoutreference to regeneration. FIG. 4 indicates the theoretical motorcurrent as a function of time in each of the motor windings a, b, and c.The current waves as illustrated do not show ripple caused by the a-clines or overlap during commutation. The current is shown for oneelectrical cycle referred to the motor windings, i.e., one-half ofarevolution of a four-pole motor. The timing interval is dependent on themotor speed and bears absolutely no relation to the a-c power linefrequency.

When current is flowing into motor terminal M 1, FIG. 3, the current isbeing supplied through one of the SCRs 19, 20, or 21, throughcorresponding input line A11, B11 or C11. The operative SCR is dependentupon the relative polarity of the ac lines at any instant, as well asthe output of the phase control rings 73 and 77, FIG. 2, which alongwith the position logic circuits 54 and 55 develops the group-enablingsignals applied to the gate drivers 64-69.

To this end, one phase control output is channeled to, for example, SCRs19, 25 and 31, FIG. 3; however, the output signal from the positionsensor 38, FIG. 2, determines which of these three SCRs actuallyreceives a gate signal. In other words, each gate signal is a functionof the a-c line phase voltage and the position of the shaft of thedriven motor. At any instant of time, two phase control outputs arepresent as are two driving gate signals.

FIGS. Sa-Sc graphically represent a possible sequence of positioncontrol signals, phase controls signals and SCR gate firing signals. Thetotal time base for FIGS. 5a5c shows one electrical cycle of themachine. Assuming that the machine is a four-pole machine and that theline frequency is 60 Hertz, the indicated speed is 360 rpm.

Motor 10 counter-emf at no load is shown in FIG. 6. For maximumproduction of torque, current must flow against the maximum counter-emf.For example, referring to FIG. 6, cur rent flow would be initiated intomotor winding a at 60. For the first 60 interval, that is, from 60 tol20it would flow out of winding b and for the next 60 interval to 180)it would flow out of winding c. However, the position sensor 38, FIG. 2,is advanced so as to effect commutation with counter emf.

A commutation event is illustrated in FIG. 6 by the shaded area betweenand and FIGS. 7a a and 7b illustrate the motor currents for motoring andregenerating commutation, respectively, at 30 advance.

The original current is designated i, and the desired current is i,. Bysetting up a circulating current i the current in leg a will go to zerowhen i becomes equal to i This is initiated by enabling the group ofSCRs which feeds current into motor winding b through SCR group 21.Concurrently, the gate signals are removed from SCR group 11 and themotor voltage Vl-2, that is the voltage across windings a, b, ifpositive, would cause the fictitious current i to flow. By enabling theSCR group 21 at 180 on the CEMF chart, it can be seen that the voltageVl-2 starts to go negative. Since this would impede commutation, thesignal enabling SCR group 21 is advanced by 30 for commutation asrepresented by the shaded area of FIG. 6 representing volt-seconds.

As hereinbefore noted with reference to FIG. 3, the 18 SCRs areconnected together in groups of three so that there is a total of sixgroups, each one of which is partially under control of one of theposition sensor outputs, through the position logic 54 and 55, FIG. 2,and gate logic 60 circuits. For convenience, the position sensor outputsare labeled P1, P2, P3. The use of a three track position sensor systemarranged so that only one output of the three changes at any instantavoids ambiguity attransfers. The three track information isconveniently converted to 6 track information in the position logicstages 54, 55, the outputs of which control the gate logic 60.

The firing control is implemented in the position logic stages 54 and 55by NAND circuits. Direction of rotation is controlled by the F (forward)and R (reverse) output signals of flip-flop 58. F equals 1 when R equalszero and vice-versa, so that F is on for forward motoring orregeneration when the motor is rotating in a reverse direction.

As shown in FIG. 8, the position logic stages comprise 12 NAND circuits90-101, each of which receives a position signal P1, P2 or F3, aninverted position signal P 1, 1 2 or 1 3 and either a forward (F) or areverse (R) rotation command signal from flip-flop stage 58 of FIG. 2.The output signals from the position logic NANDS 90-101 are applied tosix 2 input NAND circuits 102-107. Stages 102-104 have their outputsapplied to the gate drivers which control the SCRs conducting current tothe motor 10. Stages 105-107 control the SCRs conducting current fromthe motor 10 to the a-c input. The output of each gate logic stage isapplied to each of the gate drivers of a group. For example, the outputof stage 102 is applied to gate drivers 108-110, the output of 103 isapplied to gate drivers 111-113. Gate drivers 114-125 are similarlyenabled.

Thus, the gate logic NAND circuits 102-107 sift the position anddirection selection signals down to six signals which enable the SCRgate driver groups I-VI, FIG. 2, as required. These enabling signalsalong with the phase control signals A1, 1)81, Cl and A0, B0, C0 fromthe phase control ring circuits 73 and 77 control the gate drivercircuits 64-69.

While the above operation has been described with respect to use of 30advance, it should be apparent that increase of phase advance ispossible. For increased torque, 45 advance is desirable. However with 45advance, the position SCR group enabling is shifted by 90, and sixposition detection per electrical cycle for both directions of rotationis impractical. Resort may then be had to detecting 12 or morepositions. This could be achieved by four tracks (2 16) or six tracks (264 In an arrangement using six tracks, the head of the three tracksensors may be duplicated. It should be apparent however that changes inlogic from the three track system would require certain changes in theinternal logic in setting up the proper cyclic code. I

As shown in FIG. 5, a particular phase-control output may be called uponto fire more than one SCR before the next phase-control output goes on.This requires that the phasecontrol signals be continuous for 120 of thea-c line and not of the motor frequency. Also, the phase-control signalsmust be capable of being phase shifted by 150 to cover a full motoringto a full regenerating range with a 30 commutation margin.

The logic 'thus far described permits operation in the first and fourthquadrants. F/R flip-flop stage 58, FIG. 2, provides a forward/reverse(P/R) signal which establishes the desired direction of rotation.Assuming the drive is set up for forward motoring and the drive motor 10is driven in a reverse direction by an external force, regeneration isachieved.

With reference to FIG. 7a, as hereinbefore noted, SCRs of group 11,i.e., -SCRs 19, 20, and 21, are enabled from 30 to 150. At 150 to 270,SCRs 25, 26 and 27 of group 21 are enabled. In the vicinity of 150, theoutgoing group is 30 and SCRs 34, 35 and 36 are enabled. In the reverseor R mode, SCRs 25, 26 and 27 of group 21 are enabled from the 30 to 150interval. SCRs 31, 32, and 33 of group 31 are enabled from 150 to 270and SCRs 22, 23 and 24 of group 10 are on in the vicinity of 150. Justprior to 150", motor terminal M1 is positive with respect to M2 andpower could be transferred from the motor to the line through SCR groups21 and 10. The phase control is phased back so that the motor is lookinginto a negative voltage. Phasing forward decreases the negative voltagethat the motor sees and the regenerative current increases. Phasingforward far enough results in a net power flow being from the line tothe motor (plugging). If, during this process, the direction isreversed, the motor voltage has changed phase by 180 and the positivevoltage is sending current against the less positive CEMF so that thedrive is in a motoring mode.

The above description ignores leg-to-leg commutation in the motor.However, referring to FIG. 7b, it will be recalled that at 150,rectifier group 31 is enabled and motor terminal M2 is positive withrespect to motor terminal M3. This causes the current i the fictitiouseommutating current, to flow.

When i becomes equal i the commutation is completed. In motoringcommutation with 30 advance, the open circuit voltage at the inceptionof commutation is one-hall the max-- imum voltage and decreases to zero30 later. In regenerating commutation, the voltage is also one-half ofthe maximum, but increases with time. Thus, more current can becommutated in the regenerative mode. This is similar to the situationthat occurs with a 45 advance.

A transition from generating to motoring can be made smoothly with nochange in the enabling signal if the motor changes direction in theprocess. With a transition from motoring to regenerating with no changein direction of rotation of the motor 10, the enabling scheme is changedto accommodate selective rotation. A change of enabling always involvesturning on an outgoing group when its companion incoming group is on orvice-versa. This results in short circuiting the line with the choke. Toavoid the short circuit, the changes are locked out until the currenthas been reduced to zero which is effected by its feedback phase controland coordination circuits.

All of the 18 SCRs 19-36 are used in each quadrant of operation and thesame phase control operates in all quadrants.

The phase control system comprises a Delta-Wye phasing transformer stage47, FIG. 2, which is used for developing synchronizing voltage outputsapplied to the timing stage 76 and phase control ring stages 73 and 77.The ring stages are shown in greater detail in FIG. 9. Each phasecontrol ring stage is identical and includes six transistors 126, 127,128, 129, and 131 operably arranged in pairs to provide the phasetrigger outputs A1, d Bl, C1 and A0, B0, C0 to the gate driver stages.For convenience, the output terminals 141, 144 and 145 are indicated ashaving both the A and 41B phase control signals; however, it should beapparent the ring 73 develops signals Al, B1 and C1 while ring 77develops the A0, B0 and C0 output signals.

To this end, one sync input B12 or B02 is applied through diode 132 andseries connected resistor 133 to the base of input transistor 126. Thebase electrode of transistor 126 is connected to the junction ofresistor 134 and the parallel combination of resistor 135 and diode 136,which form a voltage divider across the 20 v supply connected topositive bus 137 and common line 138. The collector electrode oftransistor 126 is connected to bias the base of transistor 127 throughdiode 139. The base of transistor 127 also has applied thereto a triggerpulse input 81/80 from phase control timing stage 76 The trigger pulseBl/Bo applied to the base of transistor 127 through resistor 140 and thediode 139 serves to turn the transistor 127 ON. An output signal A1lA0is developed and taken at terminal 141 connected to the collectorelectrode of transistor 127. The collector electrode of transistor 127is returned to the base electrodes of transistors 129 and 131 throughseries resistor-diode combination. The collector electrode of transistor131 is returned to the base of transistors 127 and 129 through similarseries resistor-diode combinations. Likewise, transistor 129 also hasits collector returned to the base electrode of transistors 127 and 131to complete the ring. The transistors 127, 129 and 131 have theirrespective bases connected to a negative supply line through resistor142 and its counterparts and their respective collector electrodesconnected to a positive bus 137 through resistor 143 and itscounterparts.

In operation, assuming an output Al at terminal 141, transistor'127 isbiased OFF. In the meantime, transistors 129 and 131 are ON to clampterminals 144 and 145 at essentially ground or common potential. Toobtain an output at terminal 144, (4181), a trigger pulse is applied tothe base of transistor 127 and with the proper sync pulse applied totransistor 126 transistor 127 is caused to turn ON.

With terminal 141 clamped to common potential, transistors 129 and 131start to turn OFF. Capacitor 148 insures that transistor 129 turns OFFfirst by delaying the turnoff of transistor 131. When transistor 129turns OFF the potential at terminal 144 will hold transistors 127 and131 ON by way of the associated resistor-diode combinations. Theinterconnection of transistors 127, 129 and 131 is such that only one ofthem can be OFF at any time so that a voltage appears at only one of theterminals 141, 144, or 145. Turning the OFF transistors ON will causethe next transistor to turn OFF. Capacitors 146-148 insure propersequence.

Transistors 126, 128 and 130 clamp the unwanted pulse. These transistorsare normally ON and clamping, except when the sync input is negativeenough to overpower the ON bias of resistors 134. When a Al signal isdesired, the trigger pulse is used to turn off the previous output whichin this case is C1, and the trigger pulse A1 is directed to the base oftransistor 131. The A trigger pulse is on the same line, but is clampedby transistor 130. Sync voltages are developed by the phasingtransformers 47, FIG. 1. Trigger pulses on the same line as A1 and A0are 180 electrical degrees apart with respect to the a-c input.

In order to determine the momentary phase condition of the power line,transformer means is used as a part of a phasesensing expedient. At theconvenience of the circuit designer, either three separate transformerscan beused, one for each phase, or a single three-phase transformer canbe used. The present illustrative embodiment, as shown in FIG. 10, is ofthe former type and uses three phase sensing transfonners 1T, 2T and 3T.These transformers have their primary windings 149, 150 and 151delta-connected to the power lines A, B and C, with star-connectedsecondary windings such as 152, including a neutral center labelled 0."The windings of the secondary are respectively labelled A A,, B B and CC, at their output terminals. The primary and secondary windings aremagnetically coupled through permeable cores 1T, 2T, 3T, so that theoutputs at the above listed six terminals of the secondary 152 haveamplitudes and polarities which change instantaneously as the powerlines A, B" and C" proceed through their excursions at line frequency.The outputs at these six terminals of the secondary 152 are used tosupply information to the switching logic 37, FIG. 1, to identify whichof the phase legs in FIG. 3 should be supplying power to the motorthrough the SCRs at any particular instant of time.

These outputs A A B B, and C C are connected as shown in FIG. 10 tothree phase shift filter circuits 153, 154 and 155, one of which isconnected to each of the secondaries. Each of the six outputs from thesecondaries 152 of the phasing transformer is shifted at least once. Forexample, A11 is voltage A1 with a single shift, A01 is voltage A0 with asingle shift. A12, A02, etc., are phasing signals with additional shiftsprovided for alternate trigger pulse suppression.

Each phase shift circuit includes resistors 156 and 157 connected at oneend to the output terminals of a secondary winding. The other ends ofresistors 156 and 157 are connected directly to their output terminalsA11, A01, respectively, and also through resistors 158, 159 to outputterminals A12 and A02. Capacitors 160 and 161 connected between thecommon terminal and the other ends of resistors 156 and 157 reduce noisespikes appearing on the phasing signals with single shifts. Similarly, acapacitor such as 162 is connected between the output terminals A12 andA02.

The phase control timing circuit 76 of FIG. 2, and detailed in FIG. 11,provides three trigger outputs Al/A0, B1/B0, Cl/C0 at terminals 170, 171and 172, respectively. Each output has output pulses at 180 intervals.One pulse is for phase control ring 73 (qSAl, B1, C1), and the otherpulse is for phase control ring 77 (A0, B0, C0). A control signal isapplied at terminal 88 to the base of transistor 173 connected in anemitter-follower configuration. The collector electrode of transistor 13is connected to the positive bus 174 through voltage dropping resistor175. The emitter is coupled directly to each of three resistors 176 inthe A, B and C trigger circuits. All trigger circuits are identical and,thus, reference will only be made to the A circuit.

Transistor 177 controls the charging current of capacitor 178 which isconnected between the collector electrode and the resistor 176. Theemitter electrode of transistor 177 is connected to the positive busthrough resistor 179. Bias voltage to the base electrode is suppliedthrough its voltage divider comprising resistors 180, 181 and 182 seriesconnected with a diode 169 between the positive bus 174 and the commonreturn line 183.

The pedestal signal from transistor 173 may be suppressed by turning ONclamping transistor 184 which has its collector electrode connected tothe junction of diode 168 and capacitor 178 through diode 185. Theemitter electrode is returned directly to the common line, and the baseis connected through a pi filter, resistor 186 and diodes 187 to triggerterminals 188, 189.

The slope of the ramp voltage of capacitor 178 is controlled bytransistor 177 and is applied to the base of transistor 199 whichcontrols the charging of capacitor 191 through its emitter-collectorjunction and resistor 192. Capacitor 191 is permitted to charge to avoltage value somewhat below the sum of the ramp and pedestal voltages.This voltage value initiates firing of the unijunction transistor 193,and capacitor 191 discharges through diode 194 to provide energy for thetrigger pulse. The trigger pulse is applied to terminal and is takenacross the resistor 195 connected to the lower base, as viewed in thedrawing, of the unijunction transistor 193. The other base electrode isreturned to the positive bus through a resistor 190 and a transistor 196connected in an emitter-follower configuration. The base of transistor196 is connected to a potentiometer 197 in a voltage divider stringwhich permits adjustment of the voltage across the unijunctiontransistor 193.

Transistor 198 is used for synchronization and assures a tail end pulse.To this end, the base electrode of transistor 198 is connected throughresistors 200 and 205 and through diodes 201 and 202 to input terminals203, 204. To this end terminals 203 and 204 have applied thereto a-cvoltages which are phase displaced by Twice during a cycle there is notenough negative voltage to overpower the base supply from the positivebus and the unijunction transistor 193 dips. Balance of the phases isadjusted by controlling the ramp slope through the setting of rheostat182 in the base circuit of transistor 177 and by adjusting thepotentiometers 197 so that the unijunction transistors 193 in all phasesfire at the same voltage.

Once the correct phase control and enabling signals are available theproper gate signals are generated in the position logic stages 54, 55 ofFIG. 2 and in the gate logic stage 60. Referring to FIG. 12, theposition logic stage is based on NAND type circuits, each adapted toreceive a forward (F) or reverse (R) signal input at terminal 210, aposition signal P at terminal 211 and an inverted position signal I atterminal 212. The signals are applied through diodes 213, 214 and 215which have their anodes connected in common to the base of transistor216 through a resistor 208. Resistors 217, 218 and 219 establish theproper bias levels for transistor 216 operation, and the output is takenfrom the collector and applied to terminal 220.

This output forms one input on the terminal 220-,F of the two input gatelogic stage shown in FIG. 13. Since this input corresponds to the group11 SCRs for forward operation, the other input at terminal 220-R mustcorrespond to the group 31 SCRs for reverse operation and is derivedfrom position logic stage 98, as shown in FIG. 8. The gate logic stageis essentially the same as the position logic with the exception of oneless input. The inputs are applied through diodes 221, 222, and resistor223 to the base of transistor 224 which is operably biased throughresistors 223, 225 and 227.

The output of a gate logic stage is applied to its gate driver, aschematic representation of which is shown in FIG. 14. Each gate driverdrives an associated SCR and receives both position control informationfrom the gate logic circuits at terminal 228, and phase controlinformation at terminal 229 from the phase control ring. The circuitresembles a NAND configuration and the impulses are applied throughdiodes 230, 231 and resistor 232 to the base electrode of transistor233. Bias levels are established by resistors 232 and 235. The output oftransistor 233 is inverted from a normal NAND, because the outputsignals are applied to a primary winding 234 of an associated gatetransformer by completing a path to common or ground. The signal is ON,i.e., the transformer is pulsed, when the position and phase controlinputs are ON (not grounded). Resolution may be improved by capacitor236 which generates a head end pulse. Capacitor 236 is charged throughresistor 237 by the 20 v d-c supply. The supply may be delayed tosuppress gate pulses until all logic stages are in their proper states.Resistor-capacitor network 238 and capacitor 239 may be provided in theevent of excessive noise feedback from the pulse transformers.

The oscillator stage 71, FIG. 1, is shown in detail in FIG. 15. Theoscillator trigger circuit includes a transistor 240 connected to drivethe feedback transformer 241 to provide a trigger signal at terminal242. An LC pi network 243 is used to store enough energy so that thepower supply need only deliver the average power. The 20 volt d-cdelayed supply is also used for application of the input power to theoscillator. The repetition rate of the oscillator is advantageously setat about 20 KC, with a pulse width of about l micro seconds. Thefrequency and repetition rate are set by core 244 and resistors 245 and246.

Referring to FIG. 18, there is illustrated the position inverter,direction sensing and flip'flop stages 52, 56 and 58, respectively, ofFIG. 2. The position inverter 52 includes three inverting amplifiersincluding in the preferred embodiment shown in FIG. 18, transistors 250,251 and 252, each ofwhieh receives a position signal. Signal P1 isapplied at terminal 253 and the inverted output P 1 is taken at terminal254. Likewise, signals P2 and P3 are applied at terminals 255, 256 andthe inverted outputs P2 and P3 are taken at terminals 257, 258,respectively. Each stage is biased through its collector resistor 259and base resistors 260 and 261.

The direction sensing stage 56 of FIG. 2 is detailed in FIG. 18 justbelow the position inverter, as viewed in the drawing, and includes aflip-flop circuit comprising transistors 265 and 266 and aclamping'circuit comprising transistor 267. Inputs P1, P2 and P3 arecoupled from input terminals 253, 255 and 256, respectively, of theposition inverter to the flip-flop and clamping circuit. To this end,terminal 253 is connected to the base electrode of transistor 265through capacitor 268, resistor 269 and diode 270. Terminal 256 issimilarly connected to the base electrode of transistor 266 viacapacitor 271, resistor 272 and diode 273, and terminal 255 is connectedto the base of transistor 267 via diode 274 and resistor 275. Resistors277, 278 and 279, provided between the base electrodes and the negativebus 276, and resistors 280, 281, 282 connected between the transistorsbase electrodes and common bus 283 st the bias of the base. Resistors284 and 285 connect the lower ends of differentiating capacitors 268 and271 to the common line 283. The collectors of transistors 265 and 266are returned to positive bus 286 via resistors 287 and 288,respectively. The collector electrode of transistor 265 is coupled tothe base of transistor 266 via resistor 289. Resistor 290 couples theoutput from transistor 266 to the base electrode of transistor 265.Diodes 291 and 292 couple the collector electrode of transistor 267 tothe input differentiating circuit connected to terminals 253 (P1) and256 (P2), respectively.

In operation, transistor 267 clamps the trigger pulses coming into theflip-flop and is turned ON by a position signal P2 at terminal 255. Whenthe P2 signal is OFF, there are positive going changes at either ofterminals 254 or 258, depending on the direction of motor rotation. Ifthe motor is being driven in the forward or clockwise direction, forexample, a positive going change is reflected by position sensor P1providing a positive going Pl signal at terminal 253 while thetransistor 267 is OFF.

This P1 signal is differentiated by the RC network 268, 269 and directedto the base of flip-flop transistor 265. Transistor 265 is turned ONplacing terminal RD at essentially ground or common potential. Since thebase electrode of transistor 266 is coupled to the collector, transistor266 is turned OFF by the voltage across resistor 279 connected to thenegative bus. An output is taken at the FD terminal indicating the motoris being driven in the forward direction.

If the motor is driven in a reverse direction, a positive going signalP3 is generated by position sensor 38, FIG. 2, while the transistor 267is OFF. This signal appears at terminal 256 where it is differentiatedand directed to the base of transistor 266. Transistor 266 is driven ON,returning FD to ground potential, transistor 265 is turned OFF and anoutput is taken at the RD terminals indicating reverse rotation of themotor. The RD and FD output signals are applied via line (FIC. 2) to thecoordination circuit 84 which is shown in detail in FIG. 17, andhereinafter described.

The coordination circuit is capable of controlling the motor in fourquadrant operation. In addition to the FD and RD signals applied fromthe direction sensing circuit, a voltage feedback signal developed byrectifier 44, FIG. 2, and a current feedback signal from stage 42 areapplied to control the coordination circuit 84 in response to the demandof the reference signal introduced at input 87.

The current feedback circuit provides a double function. In addition toproviding a voltage proportional to current flow in the A," B, and C"lines, it also provides a clamp for the F/R flip-flop 58 andcoordination control. Referring to FIG. 16, terminals 295, 296, 297,298, 299 and 300 are connected across the output windings of threecurrent transformers (not shown) each of which is associated with one ofthe input lines A, B or C. The output of each of the currenttransformers is rectified by diode networks 301, 302, 303 which havetheir outputs connected to a common junction point 304 so that therectified outputs are summed. The resultant signal is directed to thebase electrode of clamping transistor 305 through resistor 306. Terminal307 provides a pick-off point for a current feedback and/or currentlimit signals. Impedance networks 308, 309 and 310 may be connected toterminal 307 as indicated by the dash lines to change the voltage andshunt away some of the current from the base of transistor 305 to permithigher current drives. Diodes 311 and 312 are operably connected to thecollector electrode of transistor 305, which has its emitter electrodereturned directly tothe common line. Diodes are series-connected betweenthe resistors 308, 309 and 310 and the common line. These diodescompensate for the base-emitter drop of the transistor 305 so thatclamping occurs at low currents if the range clamping impedance networksare connected into the circuit.

Voltage rectifier 44, FIG. 2, is a conventional arrangement, but itshould be noted that further processing of the voltage feedback isnecessary to the operation of the circuit since no phase sequencedetection is provided for detecting direction of rotation from the motor10 terminal voltage.

FIG. 17 illustrates schematically the coordination control circuit 84,FIG. 2, of the present invention. The FD and RD signals are applied atterminals 315 and 316, respectively, which are connected throughresistors 317 and 318 to the base electrodes of transistors 319 and 320.The emitter electrodes of transistors 319 and 320 are returned directlyto the common of ground bus 321, while the collector electrodes areseparately connected through resistors 322 and 323 to the input terminal324 which receives the voltage feedback signal from the rectifier 44 ofFIG. 1. The outputs of transistors 319 and 320 in FIG. 17 are taken fromthe collector circuit and coupled via diodes 315 and 326, respectively,to the base electrodes of transistors 327 and 328.- I

Transistors 327 and 328 provide speed and direction control and includethe usual zero and dead band adjust potentiometers 329 and 330connectedin the circuit between positive bus 331 and the negative (-20v)bus with resistors 332, 333, 334, 335 and 336. The base electrode oftransistor 327 is returned to a voltage divider comprising referencecontrol 337 which establishes a positive or negative reference signal.

1. In an adjustable speed drive system including a plurality ofcontrollable rectifiers for coupling a polyphase a-c electric powersource and a polyphase motor including a rotor for rotation within andrelative to stationary armature windings, rotor position sensing meanscoupled to the rotor for developing sequential position signalsindicative of the angular position and direction of rotation of therotor, phase-sensing means coupled to the a-c electric power source forgenerating sequential phase signals each indicating that a respectiveone of the phases has attained a predetermined polarity and magnitude,improved control means for controlling drive system operation throughouta full reversible range of motoring and regenerative operation, saidimproved control means comprising: a command signal source forgenerating a reference signal having a polarity and magnitude indicativeof a desired level of motor performance within a range of permissibleperformance, a performance signal source coupled to the motor and saidcommand signal source for generating a performance signal having apolarity opposite to that of the reference signal and a magnitudeindicative of the actual level of motor performance within the range ofpermissible performance, the absolute magnitude of the performancesignal for any given level of actual performance being substantiallyequal to the absolute magnitude of the reference signal indicative ofsaid given level of motor performance, first means coupled to thecommand signal source and the performance signal source and beingresponsive to a reference signal and a performance signal for generatinga comparison signal having a magnitude proportional to the sum of thereference and performance signals, second means coupled to said firstmeans, said command signal source, and said rotor position sensing meansfor receiving therefrom as input signals the comparison signal, thereference signal, and the position signals for generating in responsethereto a first output signal when the input signals are consistent withdrive system operation in either the forward motoring mode or thereverse regenerative mode and for generating in response thereto asecond output signal when the input signals are consistent with drivesystem operation in either the forward regenerative mode or the reversemotoring mode, and firing signal generation means coupled to said secondmeans and being responsive to first and second output signals therefromto generate and supply firing signals to the controllable rectifiers ina first sequence in response to the first output signal and to generateand supply firing signals to the controllable rectifiers in a secondsequence in response to the second output signal, said firing signalgeneration means also being coupled to said first means, saidphasesensing means, and said rotor position sensing means for receivingtherefrom the comparison signal, the phase signals, and the positionsignals and being responsive thereto to control the rate of powertransfer between the a-c power source and the motor.
 2. An adjustablespeed drive system as defined by claim 1 further including currentsensing means coupled to the a-c power source for generating feedbacksignals representative in magnItude of the current flow through selectedones of the controllable rectifiers, the feedback signals being coupledto said second means to permit changes in firing signal sequence onlywhen the current flow is at a level at which the change in sequence maybe made without damaging changes in current flow.
 3. An adjustable speeddrive system as defined by claim 2 including, additionally, a reactorhaving a center-tapped winding per motor armature winding, the centertap of each of the windings being connected to a respective one of themotor armature windings, a first end tap of each center-tapped windingconnected to a plurality of controllable rectifiers poled in a firstdirection and a second end tap of each center-tapped winding connectedto a like plurality of controllable rectifiers poled in the oppositedirection, the plurality of controllable rectifiers in each instancebeing equal to the number of phases comprising the a-c electric powersource, each reactor winding thereby conducting electric power in afirst direction with respect to the motor between the center tap and thefirst end tap, and in a second direction with respect to the motorbetween the center tap and the second end tap as governed by the firingof the oppositely poled controllable rectifiers associated therewith andintroducing a current limiting impedance between the oppositely poledcontrollable rectifiers as added protection therefor in the event of amalfunction.